from: "Essay on Man; Epistle II" by Alexander Pope (21 May 1688 – 30 May 1744)

Extremes in nature equal ends produce,
In man they join to some mysterious use;
Though each by turns the other’s bound invade,
As, in some well-wrought picture, light and shade,
And oft so mix, the difference is too nice
Where ends the virtue or begins the vice.

   Fools! who from hence into the notion fall,
That vice or virtue there is none at all.
If white and black blend, soften, and unite
A thousand ways, is there no black or white?
Ask your own heart, and nothing is so plain;
’Tis to mistake them, costs the time and pain.

   Vice is a monster of so frightful mien,
As, to be hated, needs but to be seen;
Yet seen too oft, familiar with her face,
We first endure, then pity, then embrace.

But where th’ extreme of vice, was ne’er agreed:
Ask where’s the north? at York, ’tis on the Tweed;
In Scotland, at the Orcades; and there,
At Greenland, Zembla, or the Lord knows where.

No creature owns it in the first degree,
But thinks his neighbour farther gone than he;
Even those who dwell beneath its very zone,
Or never feel the rage, or never own;
What happier nations shrink at with affright,
The hard inhabitant contends is right.